A pending payment will have been sent to the wrong email address, if you log into paypal and click on the payment you can see the address it has gone to. Send seller a copy of this (wrong) address, they will then need to add this in their paypal account so they can access the money. I presume they typed in the wrong email address. At present your seller hasn't received payment so this could be why they haven't sent the item.

it could be that paypal for reasons best known to themselves have sent payment by e-cheque, it happened to buyer of mine suddenly everytihng was e cheques though had money in papyapl used it daily for years gltches sometimes just happen

This happened to me. Was really annoyed as it was an item I really wanted. I contacted the Seller several times, letting them know that Ebay has access to all corespondence between us... nada. I contacted Ebay and then left negative feedback saying what had happened. Eventually Ebay removed the item from my "pending". Never heard again.